In the drilling of oil, gas, or other types of wells, tubular members such as drill pipe or production tubing are employed and typically the borehole is lined with tubular members such as casings. The casing prevents collapse of the borehole, avoids contamination of the producing strata and avoids contamination or leak off of the produced fluid or gas. Tubing or drill pipe comprising threadedly interconnected segments of pipe is employed to raise and lower or run tools within the casing and in the drilling of the borehole prior to the location of the casing within the borehole. The removal of such tubing or drill pipe when stuck or inadvertently released in the borehole is typically accomplished with a releasing spear which engages the internal diameter of the tubing member. The removal of casing or other tubular members from the borehole when required is a difficult and time consuming operation. Typically a releasing spear which includes an expandable grapple oriented on a mandrel is employed. The grapple fits closely within the tubular member to be removed and is set by releasing of the grapple from a support so that pulling upwardly on the mandrel forces the expandable grapple into contact with the interior diameter of the tubular member.
The connection between the grapple and mandrel is such that tension on the mandrel forces the grapple to expand into engagement with the tubular member. Since such releasable spears rely upon tension on the mandrel to maintain the engagement between the expandable grapple and the tubular member, if tension on the pipe string supporting the mandrel is not maintained or compressive forces are applied, engagement of the tubular member by the grapple can be lost.
The lock-down releasable spear assembly and method of the present invention provides for locking of a grapple within a section of a tubular member such that the engagement of the grapple with the interior diameter of the tubular member is not released by neutral or even compressive loads upon the supporting pipe string. Thus, the lock-down releasing spear assembly of the present invention prevents the tubular members from becoming released from the grapple due to loss of tension. The lock-down releasable spear assembly of the present invention provides for locked engagement of a grapple with the interior diameter of a tubular member.